This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Although belonging to a quite different family (the Lycopodiaceae), the Selaginellas are popularly regarded as Ferns, and are culturally treated as such. There are over 300 species known, one - S. spinosa (or selaginoides) - being a native of Britain. The plants are easily recognized by the stems bearing four rows of scalelike leaves - two rows of small ones on the upper surface, and two rows of larger ones at the sides - one large leaf and one small one arising at each joint The reproductive organs - sporangia - are borne at the tips of the shoots in angular conical spikes (fig. 316c). There are two kinds of sporangia - "mega-sporangia" and "microsporangia". Each megasporangium usually contains four large "megaspores" or "macrospores", and each microsporangium contains a large number of small microspores (fig. 316). The latter are usually borne in the axils of the upper scale leaves, while the former are in the axils of the lower. The process of fertilization is practically the same as in the Ferns (see p. 213).
Section of Spore-bearing Cone, showing Megasporangia on left and Microsporangia on right.
Fig. 316. - Selaginella inoequatifolia.
Comparatively few Selaginellas are grown on a large scale for market. They require a close moist atmosphere, and will flourish in a light compost suitable for Ferns generally. Propagation is effected either by cuttings of the stems having rootlets or by spores. Among the smaller-growing kinds worthy of notice are S. apus or apoda, S. coesia or uncinata, S. Kraussiana (or denticulata), and its varieties aurea and variegata. These grow from 1-3 in. high, and have trailing stems and an ornamental mosslike appearance. The true S. denticulata, from the European Alps, is a slower-growing kind than S. Kraussiana, and is almost hardy. S. Emiliana grows about 9 in. high, and S. Martensi and its variegated form are good free-growing plants. 8. Emiliana aurea is a golden form raised by Messrs. J. Hill & Son. It is becoming one of the most popular for market work. The same may be said of perelegans. S. amoena, a variety of caulescens, however, is the best of all, and is a very charming kind. Of the variegated kinds, 8. Watsoniana, with silvery-white shoots, is one of the best.